Low profile open-ended waveguide antenna with dielectric disc lens



March 18, 1969 L. G. PETRICH ,1

LOW PRO I E OPEN-ENDED WAVEGUIDE ANTENNA Y C RI g I L C DISC LENS EPLANE H PLANE FIG.2

VENTOR.

MHDZ 7- h C .m Em D.. G .5 u 0 L United States Patent 9 Claims ABSTRACTOF THE DISCLOSURE This invention relates to a low-profile microwaveantenna, with a dielectric surface-wave configuration. The antenna takesthe form of a slightly conical, circular, dielectric disk in contactwith a metallic ground plane. The ground plane is embedded with circularchokes.

There existed the need for a low-profile, (and consequently lowaerodynamic drag), high-temperature, X- band antenna having a very wideomnidirectional beam, for use on the Nike-Zeus missile. The instantinvention is the fulfillment of this need. A pair of antennaeconstructed as defined hereinafter will provide isotropic coverage, whenproperly mounted on a missile.

The invention takes the form of a slightly conical, circular, dielectricdisk in contact with a metallic ground plane imbedded with circularchokes.

An object of the invention is to provide a novel lowprofile microwaveantenna.

Another object is to provide a novel, dielectric, surfacewave, microwaveantenna.

Yet another object is to provide a novel, high-temperature microwaveantenna.

Still another object is to provide a novel microwave antenna having avery wide omnidirectional response pattern.

These objects, and others which may be obvious from the followingdescription, are best understood by reference to the drawings, in which:

FIGURE 1 is a full sectional view of the inventive antenna, and

FIGURE 2 is a response curve for the antenna of FIGURE 1.

Referring now to FIGURE 1, the antenna of the invention consists of aslightly conical dielectric disk in contact with a metallic ground plane11. The disk 10 and ground plane 11 are mounted on the end of a circularwaveguide 12. It is to be understood that the antenna is a solid ofrevolution of the FIGURE 1 section about the longitudinal axis X-X ofwaveguide 12.

Disk 10 is a high temperature dielectric such as alumina or fusedquartz, having a dielectric constant designated e.

The dimensions of the antenna elements, with respect to the desiredwavelength of operation A, are shown on FIGURE 1 of the drawings. As canbe seen from FIG- URE 1 of the drawings, the inside diameter ofwaveguide 12 is M2. The thickness of disk 10 is )t/4x/e, and the radiusof ground plane 11 from the inside of waveguide 12 to the outside of theground plane is 7\. Disk 10 is a shallow cone, the side of which isdepressed below a perpendicular to axis X-X of waveguide 12.

Ground plane 11 has a plurality of grooves, such as 3,434,146 PatentedMar. 18, 1969 13, in the surface thereof. These grooves act as wavetraps or chokes, and reduce undesired lobes in the radiation pattern ofthe antenna. The depth of the grooves is 3k/16, and the width is h to Athe depth thereof.

Attached to disk 11 is a stepped matching element 14 to provide a matchbetween the waveguide and antenna impedances.

The response pattern of the inventive antenna is shown in FIGURE 2, forthe e plane and the h plane. For these response patterns, the dielectricconstant 5:3.78. As is obvious from inspection of FIGURE 2, the patternis in the form of a very wide beam. The overall beam pattern is thesurface of revolution of the shown pattern about the 0l80 axis, and isthus omnidirectional. The 0"- axis corresponds to the X-X axis of FIGURE1.

While a specific embodiment of the invention has been shown anddescribed, other embodiments may be obvious to one skilled in the art,in light of this disclosure. The cone angle of disk 10 may be less thanthe 15 described, and may in fact, be 0". Such a change in angle willproduce a change in the radiation pattern to make it less broad, or moredirectional in the XX direction in FIGURE 1 or the 0l80 direction ofFIGURE 2.

The designation of high temperature dielectrics such as alumina or fusedquartz as the material for disk 10 is with high temperature requirementsin mind. Obviously, other less rugged dielectrics could be used andwould be within the scope of the invention, if less rugged conditionswere specified for the antenna.

If desired, a skirt portion and a flange portion may additionally beprovided for disk 10, which skirt portion would cover the exposed sideof round plane 11, and which flange portion would be coplaner with thebottom surface of the ground plane. The additional portions would give asmoother configuration to the antenna and would aid in reduction ofstresses from thermal expansion of disk 10. However, such additionalportions would cause a disturbance in the radiation pattern of theantenna by providing an unwanted path for TM mode propagation. Thisdisturbance could be minimized by making the additional portionstogether an electrical length an odd multiple of a quarter wavelength ofA, and metalizing them.

While the inventive antenna was designed for use on a missile, it wouldnot be necessary to limit its use thereto. Obviously, the antenna couldbe used on any object desired.

I claim:

1. A microwave antenna for use at a wavelength A, including a body ofconductive material in the shape of a segment of a cylinder terminatingin a cone, with an axial perforation through said cylinder and saidcone; at least one groove on said cone, concentric with the axis of saidcone; and with a sheet of dielectric material covering said cone,wherein said sheet is approximately 1)\/4\/e thick.

2. The antenna as defined in claim 1 wherein both of said cylinder andsaid cone are right circular figures.

3. The antenna as defined in claim 2 wherein the radial dimension ofsaid cone from said perforation to the wall of said cylinder is A.

4. The antenna as defined in claim 2 wherein the side of said cone makesan angle of approximately 15 with a perpendicular to the axis of saidcylinder.

5. The antennas defined in claim 2 wherein there are a plurality ofgrooves.

3 4 6. The antenna as defined in claim 5 wherein said References Citedgrooves are approximately 31/16 deep. UNITED STATES PATENTS 7. Theantenna as defined in claim 6 wherein said the width of said grooves isapproximately /2 to A of the depth- 5 2,761,138 8/1961 Sherman 343 7s38. The antenna as defined in claim 2 wherein said sheet of dielectricincludes a generally cone-shaped portion ex- I LIEBERMAN, primaryExaminer tending into said perforation.

9. The antenna as defined in claim 1 wherein said US. Cl. X.R.perforation is circular and has a diameter of M2. 10 343-772, 735

